MFH: r537613

print/harfbuzz: update to 2.6.7

Changes: https://github.com/harfbuzz/harfbuzz/releases/tag/2.6.7
ABI: https://abi-laboratory.pro/tracker/timeline/harfbuzz/
Reported by: GitHub (watch releases)
Approved by: ports-secteam blanket (required by Firefox 79)